The attack took place while the convoy was driving from the town of Dir to the nearby hill resort of Swat, they said.

Two soldiers and two officers were killed, a police official said.

Swat is a stronghold of a banned extremist group linked to radical clerics at Islamabad's Red Mosque, which security forces have besieged after deadly clashes between Islamist students and security forces.

A policeman and four civilians were killed in attacks on Wednesday in the same area.

Calls have been made on a private Islamist radio station in the area to launch "jihad" (holy war) against government officials in retaliation for the mosque confrontation.

The organisation, called Tehrik Nifaz-e-Shariat-e-Mohammadi, was banned in 2002 by President Pervez Musharraf after it sent thousands of volunteers to Afghanistan to battle US forces in support of the fundamentalist Taliban.

Meanwhile, six people were killed in a gunbattle in a Pakistani tribal area yesterday after masked assailants abducted an official from a military college, officials said.

Masked gunmen in the troubled tribal region of North Waziristan, bundled into their car Faisal Islam, an official from a military cadet college, security officials said.

The kidnappers sped away after the abduction in Razmak town but local tribesmen chased them and the ensuing gunbattle left six people dead, including four kidnappers and two tribesmen.

At least 11 others were injured.